Venetian blinds are well known and typically include a head rail, a bottom rail, and a plurality of slats arranged between the headrail and the bottom rail. The slats are typically made from a variety of materials, such as metal, wood, plastic or other materials and supported by ladders.
Such blinds also typically include a tilt mechanism to enable the slats to move from a horizontal position to a nearly vertical position to open and close the blinds to affect the passage of light. As is also conventional with such systems, flexible line members or lift cords are coupled to the bottom rail, pass through the slats and into mechanisms within an upper headrail. The cords are employed to raise the bottom rail, accumulating individual slats as the bottom rail is raised. Because of gravity, the natural tenancy of the bottom rail and accumulated slat weight is to free fall. In many instances in the prior art, cord lock mechanisms are employed to lock the cord, thereby setting bottom rail, and the slats stacked thereon at a height determined by the user. Pleated and other types of shades also include a bottom rail and include similar raising, lowering and line member or cord lock mechanisms.
Spring motors are known to be provided to assist the elevating and lowering of a variable load such as that provided by a venetian blind type window covering. Spring motors conventionally comprise a flat ribbon of spring metal which is pre-stressed and coiled so as to have a natural or relaxed state in which the spring forms a tightly wound coil disposed on or in a spring storage or take up drum. The extended free end of the coil is attached to the hub of an output or spring drive drum onto which the spring is backwound by rotating the output drum in a direction to back or reverse wind the spring thereon. When the load to which the output drum is connected is released, the curling property of the spring causes it to rewind onto or into the storage drum toward its natural or relaxed state. Such spring motors as descried above can be of constant or variable force, depending upon the intended use of the motor. The characteristics of a variable force spring motor can be obtained in varying ways, but varying the radius of curvature of the spring member along the length thereof is conventionally the preferred method.
In connection with the use of such a spring motor and a venetian blind, as an example, a control drum or spool is mounted co-axially with the output drum for rotation therewith, and the flexible member or cord is wound onto the spool in a direction which provides for the unwinding of the cord to rotate the spring output drum in the direction for winding the spring member thereon from the spring storage drum. When the force necessary for such unwinding is relaxed, the spring member returns to its naturally coiled position whereby the spring output drum is rotated by the spring member in a direction to rewind the cord or belt onto the spool. In those blinds with locking mechanism, such rewinding of the cord onto the control drum is inhibited.
When raising or lowering a load such as the bottom rail and slats of a venetian blind accumulating on the bottom rail, a pair of cords may be wound on the spool in opposite directions with the free ends of the cords attached at the opposite ends of the bottom rail. When the bottom rail is lowered, the two cords unwind from the spool thus driving the spring output drum to wind the spring member thereon. Upward displacement of the bottom rail from a lowered position results in the spring member rewinding on the spring storage drum to rotate the spring output drum and thus the control drum in the direction to rewind the two cords. In elevating the lowering a suspended load of the foregoing example type, which is too heavy to provide desire displacement characteristics in connection with the upward and downward movement of the bottom rail, and using a single spring motor, many times it is necessary to provide a larger spring motor or operate two or more spring motors in tandem.
When it is desired, the spring motor may be designed to allow the balancing of the gravitational pull on the bottom rail and accumulated slats and the resisting force of the spring motor so that the weight, even though increasing, as additional slats are accumulated on the bottom rail as it is raised, the bottom rail may be released and stay at a predetermined height. However, this is difficult under many conditions.
A variety of factors may cause the blind to have different performance characteristics upon installation, including using different materials of slats, changing the size of the blind or the amount of window covering, the number of slats in the blind, the weight of the drive actuator, the weight of the bottom rail, etc. Without the blind being configured to be adjusted at the point of sale or by the consumer after the point of sale, it may be difficult to utilize the same motors on different types and sizes of blinds, particularly when the blind is customized at the point of sale per the consumer's requirements (e.g., size dimensions, etc.).
Accordingly, it would be advantageous to provide a blind in which lifting cords and cord mechanisms are eliminated from shades or blinds and relate to window covering systems which, inter alia, employ one or more spring motors to balance the weight of the accumulated window covering material, independent of the extent to which the blind or shade is raised or lowered. It would also be advantageous to provide a blind that utilizes an adjustable drive actuator to permit the adjustment of the blind's performance characteristics at the point of sale, after the blind has been customized, at the point of installation, or the like. It would also be advantageous to provide a cordless blind which a spring motor is used to eliminate conventional pull cord and cord lock mechanism and which is adjustable so that it is suitable for encountering a wide variety of loads making it unnecessary to design a specific motor for a specific end use.
It would be desirable to provide a blind with or providing anyone or more of these or other advantageous features.